The number of connections on integrated circuits is becoming ever greater, while they are at the same time being miniaturized to an ever greater extent. The difficulties expected in the course of this increase in miniaturization in the application of solder paste and component fitment are intended to be overcome by new housing forms, single-chip, few-chip or multi-chip modules in a ball grid array package being preferred, in particular, for this purpose (DE-Z productronic 5, 1994, pages 54, 55). These modules are based on a plated-through substrate, on which the chips are made contact with, for example, via contact-making wires or by means of flip-chip mounting. The ball grid array (BGA) is located on the underneath of the substrate, and is often also referred to as a solder grid array, land grid array or solder bump array. The ball grid array comprises solder studs arranged over the area on the underneath of the substrate, which allow surface mounting on printed circuit boards or assemblies. The arrangement of the solder studs over an area allows large numbers of connections to be provided, using a large grid size of, for example, 1.27 mm.
In the case of so-called MID technology (MID=Molded Interconnection Devices), injection-molded parts with integrated conductor runs are used instead of conventional printed circuits. High-quality thermo-plastics, which are suitable for the injection molding of three-dimensional substrates, form the basis of this technology. Such thermoplastics are distinguished over conventional substrate materials for printed circuits by better mechanical, thermal, chemical, electrical and environmental characteristics. In the case of one specific direction of MID technology, the so-called technology of injection-molded parts with integrated conductor runs, the structuring of a metal layer applied to the injection-molded parts is carried out without using the otherwise normal mask technique, by means of a special laser structuring method.
In this case, a plurality of mechanical and electrical functions can be integrated in the three-dimensional injection-molded parts with structured metallization. The housing support function at the same time provides guides and snap-action connections, while the metallization layer is used for electromagnetic shielding, and ensures good heat dissipation, as well as carrying out the wiring and connection function. Further details relating to the production of three-dimensional injection-molded parts with integrated conductor runs can be found, for example, in DE-A-37 32 249 or EP-A-0 361 192.
U.S. Pat. No. 5,081,520 discloses a method for mounting IC chips on substrates, in the case of which method the substrates are produced as injection-molded parts with integrated studs for attaching the IC chips. Once the studs have been metallized, a connecting layer is applied so that the IC chips can be mounted on the substrates, the chip connecting surfaces being electrically conductively connected to the associated metallizations on the studs.
International Application No. PCT/EP95/03763 has proposed a so-called polymer stud grid array (PSGA), which combines the advantages of a ball grid array (BGA) with the advantages of MID technology. The new version was called a polymer stud grid array (PSGA) on the basis of the ball grid array (BGA), the term "polymer stud" being intended to refer to the polymer studs which are integrally formed during the injection molding of the substrate. This version is suitable for single-chip, few-chip or multi-chip modules and comprises
an injection-molded, three-dimensional substrate composed of an electrically insulating polymer,
polymer studs which are arranged over the area on the underneath of the substrate and are integrally formed during injection molding,
external connections which are formed on the polymer studs by an end surface which can be soldered,
conductor runs which are formed at least on the underneath of the substrate and connect the external connections to internal connections,
at least one chip which is arranged on the substrate and whose connections are electrically conductively connected to the internal connections.
In addition to the simple and cost-effective production of the polymer studs during the injection molding of the substrate, the production of the external connections on the polymer studs can also be carried out with minimal effort together with the production of the conductor runs, which is normal for MID technology and the technique of injection-molded parts with integrated conductor runs. The fine laser structuring which is preferred for the technique of injection-molded parts with integrated conductor runs allows the external connections to be produced on the polymer studs with a large number of connections and with a very fine grid. It should furthermore be stressed that the thermal expansion of the polymer studs corresponds to the thermal expansion of the substrate and to that of the printed circuit board accommodating the module. Should any mechanical stresses occur, then the elastic characteristics of the polymer studs allow the stresses to be at least partially compensated for. The dimensional stability of the external connections formed on the polymer studs also allows the reliability for repair and replacement to be considerably improved over ball grid arrays, whose external connections are formed by solder studs.